摘要
针对双头螺杆廓形参数难以实现高精度、高效率检测的问题,以四轴旋风铣床为载体,设计并实现了一种基于激光三角位移传感器(LTDS)的在机测量系统。为了提高系统的测量精度,基于变结构元广义形态学方法、多项式插值算法及椭圆拟合法,实现了含噪光斑图像质心的微米级提取,并进行了实验验证。为了避免最小二乘分段拟合方法在断点处不满足函数连续性和可导性的缺陷,提出了基于拉格朗日乘数法的点云信号光顺处理算法。最后根据信号重构结果实时计算廓形参数,判断加工质量。实验结果表明,设计的在机测量系统可在39.7 s内完成一个螺距的螺杆廓形参数检测,测量精度为±9μm,其中长轴、短轴、螺距的测量不确定度分别为0.72、0.69、1.65μm,显著提高了测量精度和效率。
Objective The double-headed screw rotor is a common and critical power generating component and the accuracy of its profile has a direct bearing on the mechanical properties and service life of various products.The current profile accuracy measurement methods for double-headed screw rotors are all contact-type,and are divided into two type.One type is to manually measure the profile accuracy with a single-parameter instrument such as a micrometer.Although measurement accuracy and efficiency are both low,this method can be used for on-machine measurement.The second type refers to automatic measurement of the profile accuracy with a coordinate measuring machine(CMM).Despite its high measurement accuracy,this method consumes significant auxiliary time,increases the positioning error in off-machine measurement and cannot guarantee the post-correction accuracy of a nonconforming screw.To measure the profile of double-headed screw rotors with high precision and efficiency,an on-machine measuring(OMM)system based on a laser triangulation displacement sensor(LTDS)is designed and implemented by considering a four-axis whirlwind milling machine as the carrier.Methods To improve the measurement accuracy of the system,the generalized variable-structural-element morphological method,polynomial interpolation algorithm,and ellipse fitting method are combined to realize micron-level centroid extraction from a noisecontaining spot image.Then,the hybrid method is experimentally verified.Subsequently,a smoothing algorithm for point cloud data is devised based on the Lagrange multiplier method to avoid the defects associated with the piecewise curve fitting method,that is,function continuity and differentiability cannot be satisfied at piecewise points.Finally,the profile parameters are calculated in real time according to the data reconstruction results,and the machining quality is assessed.Results and Discussions The measuring results are shown in Fig.9.In comparison with that of the traditional LTDS-based measuring method,the profile measured through the OMM method is closer to the CMM result.This outcome indicates that the LTDS data acquisition accuracy can be improved with the proposed method in Section 3.1,that is,the generalized variable-structuralelement morphological edge extraction algorithm is applied first to realize effective edge measurement of the spot image and then the polynomial interpolating subpixel edge positioning algorithm is applied to realize rapid subpixel positioning.Ultimately,centroid extraction is conducted through the ellipse fitting algorithm.As shown in Table 3,all difference values are within the acceptable tolerance zone for all three standard measuring methods compared with their corresponding nominal values,indicating that the screw rotor part is acceptable after machining.However,the proposed spot centroid extraction method can improve the measurement accuracy of traditional LTDS for a free-form surface compared to OMM.The profile accuracy of the screw rotor obtained through the proposed LTDS-based on-machine measuring system is within±9μm from the difference values between OMM and CMM results.Conclusions Such whirlwind milling machines configured with four-axis screw rotors have been placed in operation.Actual results indicate that the measurement accuracy using the proposed method is±9μm,in which the measurement uncertainties of major axis,minor axis,and screw pitch are 0.72,0.69,and 1.65μm,respectively,and measuring one screw pitch consumes 39.7 s.Therefore,the results indicate that the proposed on-machine measuring system can satisfy the requirements for accurate control and rapid measurement of large workpieces in actual operation.
作者
孙梦楠
董祉序
徐威
刘明轩
孙兴伟
Sun Mengnan;Dong Zhixu;Xu Wei;Liu Mingxuan;Sun Xingwei(School of Mechanical Engineering,Shenyang University of Technology,Shenyang 110870,Liaoning,China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2023年第14期83-92,共10页
Chinese Journal of Lasers
基金
国家自然科学基金(52005347)
科技部中央引导地方科技发展专项(2022JH6/100300015)。
关键词
测量
螺杆转子
激光位移传感器
信号处理
measurement
screw rotor
laser displacement sensor
signal processing
